A stateful remote F# Interactive over MCP with Akka.NET process/session isolation

[ingted]

https://github.com/ingted/FSharp.MCP.DevKit

I want to share a practical use of Akka.NET in an F# tooling project.

I have been working on a fork of FSharp.MCP.DevKit, where the useful part is not just “run F# code remotely”, but:

• create a remote out-of-process F# Interactive host
• keep expensive initialization alive in that host
• create multiple sessions on top of it
• run many later queries against the same initialized state
• keep process-level and session-level isolation

Akka.NET is doing real work here, not just sitting at the edge:

• Akka.Proc.Supervisor provisions and manages remote procnode processes
• each remote host is a separate process
• inside each procnode, Akka.FSI.Supervisor manages the FSI control plane
• each FSI session is coordinated through actors
• execution, evaluation, session listing, reset, and health flow through actor messages

That isolation model turned out to be very useful for long-running F# workloads. A normal dotnet fsi script.fsx loop would often pay the full initialization cost every time. With the remote host/
session model, heavy setup can run once and later queries can reuse the same in-memory state.

A few practical lessons from making this work:

• container path mapping matters a lot when the remote FSI host needs #I / #r paths
• control-plane requests like session listing should not block behind heavy execution
• long-running initialization benefits from async execution plus later evaluation on the same session
• explicit process supervision was much easier to reason about than trying to hide everything inside one server process

The original upstream project is currently on hold, but this Akka.NET-backed remote host/session approach still feels very valuable for REPL-heavy and data-heavy F# workflows.

If people are interested, I can share more details about the actor layout, proc supervision model, or the MCP integration side.

[Aaronontheweb]

So if I understand this correctly, this creates an MCP server that allows you to spawn your own interactive F# sessions on-demand from an LLM harness, with Akka.NET orchestrating and managing those processes?

[ingted]

Hi @Aaronontheweb, yes!!